Its easy to use a rotary epilator on your legs.
On the back, not so much… I don’t have much back hair at all, just a little bit on my lower back. I epilated it one time only, it was very painful, similar to epilating the armpits, and I got a ton of ingrown hairs.
I use my epilator on the arms and legs only. I have a norelco bodygroom thing that I use on my chest and other areas.
Note also that some epilators are safer to use than others, ie some of them are much more likely to grab your skin than others so you have to be more careful. I have an emjoi right now which has 4 tweezing heads on it, it works more quickly but is more likely to grab the skin than the previous one I had which was a panasonic.
my advice:
don’t get a cordless epilator, they use too much energy and the battery will die before you are done
only use the epilator after taking a hot shower and using a loofah or body scrub to exfoliate the area… the epilator grabs moist hairs better and it is less painful since the follicles are dilated by the heat.
edit: cordless epilator is ok if it can be used while plugged in also, but many of them including my old panasonic can not be used while charging